A method for detecting optical flow is well-known in the art for recognizing behavior of mobile unit using images of external environment by calculating, for example, gradient change of image density from sequence of input images.
In Japanese Patent Application Unexamined Publication (Kokai) No. 2000-171250, a method for detecting current position of a mobile unit by means of optical flow is disclosed. According to the method, optical flow of scenes of certain course are acquired every predetermined distance when the mobile unit moves along with the course beforehand. Then relationship between the optical flow and taking point is stored. After that, optical flow of the course is newly detected and undergoes matching with all of stored optical flows. The one showing maximum matching result is selected and a point associated with the selected one is recognized as current point where the mobile unit moves.
In Japanese Patent Application Unexamined Publication (Kokai) No. H11-134504, another method is disclosed. The method comprises calculating optical flow from moving images and processing the optical flow with neural network layer to recognize the behavior of the mobile unit. The method further comprises judging necessary processing based on the recognition. According to the method, detecting the approach to the obstacle is enabled with simple neural network based on moving images.
However, in order to implement the former method, many relationships between optical flow and point in a course need to be stored by moving the mobile unit in the predetermined course beforehand.
Generally, there are some problems to recognize position and behavior of the mobile unit by feature extracting based only on moving images like the latter method. For example, since relative distance between light source and a camera on the mobile unit changes continuously as the mobile unit moves, image intensity such as lightness changes so great that accurate feature extracting is difficult. In addition, since vibration of the moving mobile unit is transmitted to the camera, accuracy of feature extraction is degraded. If a recognizing system is configured to execute smoothing process over multiple frame of images to remove bad effects due to the variation of image intensity or the vibration, computing load becomes too heavy or feature extraction becomes difficult when the image moves fast due to large time variation.
It is objective of the present invention is to provide an image recognizing apparatus and method that can recognize the behavior of a mobile unit rapidly and accurately using images of external environment taken on the mobile unit in the real application.